A published paper in my RG sites on the heavy metal content on soil in a thermal power plant may be followed.

There are several analytical methods, with different equipment and extraction procedures.

However, before the laboratory part, I suggest to have a structured sampling plan, because most of the uncertainty comes from this first part and can undermined the representativeness.

Beside the above suggestions you may also look at the attached files.

Dear friends in RG who have taken the time to answer our question thank you